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Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV)
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Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV) F. Millo a,*, S. Caputo a, A. Piu b a b
Energy Department, Politecnico di Torino, Italy Centro Ricerche Fiat (C.R.F), Turin, Italy
article info
abstract
Article history:
The usage of a Fuel Cell (FC) as a range extender in a Full Electric Vehicle (FEV) is a
Received 16 November 2015
convenient solution to address the issue of the shortage of range of this type of vehicles.
Received in revised form
Compared with the Internal Combustion Engine e Range Extender (ICE-RE), the Fuel Cell e
18 April 2016
Range Extender (FC-RE) has the potential to provide power with higher efficiency (more
Accepted 18 April 2016
than 50%) and, above all, it can allow zero emissions operation of the vehicle even when
Available online xxx
the on-board power source is switched on for range extension.
Keywords:
Membrane Fuel Cell), developed in the framework of the collaborative European project
HT-PEM fuel cell
ARTEMIS (Automotive pemfc Range extender with high TEMperature Improved meas and
Range extender
Stacks), on a light duty, full electric, commercial vehicle, was investigated.
In this work, the introduction of a new HT-PEMFC (High TemperatureeProton Exchange
Battery
Firstly, a model of the Full Electric Vehicle was created and validated by means of
Electric vehicle
experimental tests carried out on rolling chassis dyno over both type approval and real
Fuel cell vehicle
world driving cycles. Once the model was developed, the effects of the introduction of an HT-PEMFC on the vehicle range was evaluated and the performances of different HT-PEM fuel cell stack systems, combined with various hydrogen storage system configurations, were compared. © 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction With a share of more than 20% of total greenhouse gasses in 2009, transport is the only source of emissions in the EU which has exhibited continuously growing in the decade 2000e2009. Besides GHG emissions, transport is also responsible for other negative externalities, e.g. air pollution and particulate matters, due to the oil-derived fuels used in the internal combustion engines.
For these reasons, the EU Sustainable Development Strategy is addressed to a balanced shift towards environmentally friendly transport modes, including the development of zero/ low emissions vehicles [1]. The usage of electric energy for powering the land vehicles represents a key step towards the reduction of the greenhouse gas and pollutant emissions. Battery Electric Vehicles (BEVs), that use a battery stack for power an electric motor, are becoming an attractive solution for Europe and US automotive markets. The BEV powertrains give the possibility to operate
* Corresponding author. E-mail addresses: [email protected] (F. Millo), [email protected] (S. Caputo), [email protected] (A. Piu). http://dx.doi.org/10.1016/j.ijhydene.2016.04.120 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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with zero emissions in the place of use (zero tank-to-wheel emissions). The advantages of using BEV are the high overall energy efficiency, thanks to energy recovery capability (e.g. regenerative braking), and the higher torque transmitted to the wheels compared to a traditional vehicle equipped with an Internal Combustion Engine (ICE). Furthermore, BEVs do not produce noise and pollutant emissions. These characteristics make them the ideal vehicles to be used in the urban areas [2,3]. Battery Electric Vehicles are also the best solution for usages that do not require long-range daily driving, as the delivery vans and city buses. Ku¨hne described in his work how the electric buses can solve energy, pollution and urban traffic problems [4]. However, pure Battery Electric Vehicles (BEVs) raise several problems that have to be overcome to make them competitive on the market, such as cost, weight, short driving range, long charging time, limited lifespan, etc. Range Extenders (REs) are one mean to enhance the driving range of BEVs using an electricity-generating equipment onto the vehicle that completes the battery energy. Nowadays, the use of Internal Combustion Engines (ICEs) as range extenders is the most exploited solution by car makers. The Internal Combustion Engine e Range Extender (ICE-RE) assists the battery's State Of Charge (SOC) in maintaining a higher level, extending the vehicle range and the overall battery life. Unfortunately, when the ICE-RE is in operation, the vehicle is not in a pollution-free mode, and, so, does not fulfil the requirements of a Zero Emissions Vehicle (ZEV) [5]. The Fuel Cell - Range Extended Electric Vehicle (FC-REEV) is a possible solution to improve the battery range maintaining zero tank-to-wheel emissions capability [6e8]. Several studies have examined the range extension of Full Electric Vehicles (FEVs) through the use of fuel cell stacks [6e15]. Le Duigou and Smatti [16] compared different powertrain technologies (ICE, BEV, HEV, FCEV and FC-RE) within a techno-economic framework. If vehicles totally based on fuel cell are still showing difficulties in the market penetration, especially for the high cost, the hybridization of fuel cell with other technologies (e.g. batteries) can reduce the life-cycle cost of vehicles, facilitating their market introduction. Moreover, the quantity of hydrogen carried on board the FC-REEV is quite low, allowing fast refuelling and low hydrogen tank weight. Besides, a small FC used as a range extender allows to reduce capacity, weight and recharging time of batteries, ensuring the same range of an equivalent BEV. In order to fully exploit the advantages of FC-REEVs, an energy analysis must be carefully performed, planning some strategies of energy management to optimize the total efficiency and safeguard the devices from excessive stress that can limit their lifecycle [17]. Corbo et al. [18] performed an experimental analysis with the scope to investigate the energy management issues of two electric hybrid powertrains for scooter and minibus applications. The experiments they have carried out on the two hybrid powertrains showed that the overall efficiency is not significantly influenced by the hybrid configuration adopted, as the efficiency values ranged from 27 to 29% in the different cases analysed. This is due to the negligible influence of load
on the fuel cell efficiency, which is the main difference with respect to an internal combustion engine. In this work, the introduction of a new High TemperatureeProton Exchange Membrane Fuel Cell (HT-PEMFC), developed in the framework of the collaborative European project ARTEMIS (Automotive pemfc Range extender with high TEMperature Improved meas and Stacks), to extend the range of a Light Duty e Full Electric Vehicle (LD-FEV), the FIAT Iveco Daily 35S, was analysed. Proton Exchange Membrane Fuel Cells (PEMFCs) offer many advantages including high power density, rapid start-up and high efficiency. The HT-PEM is assembled with phosphoric acid doped poly-benzimidazole (PBI) membranes and works between 120 C and 180 C. Unlike low temperature PEM fuel cells, HT-PEM fuel cells need no humidification and, therefore, eliminates water management issues [19]. Moreover, they are characterized by enhanced electrochemical kinetics and higher carbon monoxide tolerance. For these reasons, HT-PEM stacks can be the most suitable PEM technology for a transportation range extender [20,21]. Janben et al. [22] investigated about the performance of a high temperature polymer electrolyte fuel cell stack varying some operating parameters, as anode and cathode stoichiometry's, temperature and fuel used (pure hydrogen or synthetic reformate). In order to assess the advantages of a fuel cell range extension, a numerical model of the FIAT Iveco Daily 35S was created and validated by means of experimental tests, carried out on rolling chassis dyno at Centro Ricerche Fiat (C.R.F). The calculation tool was then used to examine the effects of the introduction of a fuel cell, which supplies the accessory loads (pumps, radiator fan, lights, cabin heater, etc.), on the vehicle range, assuming that the existing battery package is maintained and used to provide power to the electric motor. Furthermore, the benefits deriving from the usage of the new, high performance HT-PEMFC, developed in the ARTEMIS project, were assessed.
Powertrain configuration As above said, in order to test the concept of using an HTPEMFC as a range extender in an electrical, automotive application, the FIAT Iveco Daily 35S is chosen as a case study (Fig. 1). In Table 1 the technical characteristics of the vehicle are reported. The powertrain is driven by an asynchronous three phase electric motor, featuring a 30 kW nominal power (60 kW peak power) and supplied from an inverter via 2 ZEBRA® (Zero Emission Battery Research Activities) batteries. The motor is directly responsible for moving the vehicle and recovering energy while braking. In Fig. 2, a schematic of the battery electric system is shown. The battery electric system is characterized by two traction batteries (ZEBRA), used to supply the electric traction motor through an inverter and the hydro-steering pump, and a low voltage battery (12 V), used to supplies the other accessory loads, as radiator fan, water and vacuum pumps. High and low voltage lines are connected through two DC/DC converters.
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Battery pack
Fig. 1 e FIAT Iveco Daily 35S.
Table 1 e Technical characteristics of the FIAT Iveco Daily 35S.
The battery pack is composed of 2 ZEBRA® batteries (Model Z5278-ML3P-76, Rated Capacity: 76 Ah, Rated Energy: 21.2 kWh, OCV: 278 V). ZEBRA® batteries, with a specific energy of ca. 120 Wh/kg and a specific power of ca. 180 W/kg, is a good solution for mobile applications like cars, vans and buses. In the charged state, the ZEBRA® cell has a positive electrode consisting of nickel chloride and a negative electrode composed of sodium. During the discharging phase, the sodium reacts with the nickel chloride to form sodium chloride and nickel. The process takes place in the reverse direction during the charging phase. A liquid electrolyte consisting of “b” alumina is used to conduct sodium ions and to ensure the electrical insulation between anode and cathode. This sodium-ion conductivity is higher at temperature not lower than 260 C, therefore, the operational temperature of ZEBRA® batteries is in the range of 270e350 C. A second electrolyte in molten state (sodium aluminium chloride) provides the ion conducting properties inside the positive electrode [23].
Technical characteristics Vehicle characteristics
Curb Weight Full Load Weight Drag force @100kph Maximum speed Motor e generator Electric motor characteristics Nominal power Peak power Battery Batteries characteristics Battery voltage (OCV) Battery capacity Rated energy
kg kg N km/h Type kW kW Type V Ah kWh
2500 3500 1270 70 Asynchronousthree-phase 30 60 2 ZEBRA® Z5-278-ML3P-76 278 76 21.2
FEV model development The vehicle model was created with GT-SUITE, a commercially available modelling tool developed by Gamma Technologies, which allows the assessment of the vehicle performance along a driving cycle [24,25]. The model was then validated with experimental data gathered both along the European type approval driving cycle (New European Driving Cycle, NEDC) and along a real world driving cycle developed by the OEMs in the framework of the European collaborative project ASTERICS [26].
Fig. 2 e Schematic of the battery electrical system. Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Z Insta: Capacity ¼ Q0
Idt
(2)
t
Q0 ¼ SOC0 $Maximum Capacity
(3)
where Q0 is the initial battery charge, I is the instantaneous current and SOC0 is the initial value of the SOC. The battery model in this simulation study is simplified as an equivalent circuit with a voltage source and a resistance (Eq. (4)): IVOC I2 Rint C$Prequest ¼ 0
(4)
where I is the instantaneous current, VOC is the Open Circuit Voltage (increasing with the battery SOC), Rint is the internal resistance of the battery (decreasing with battery SOC), C is its Coulombic efficiency, normally applied when the battery is charging (C > 1) and Prequest is the power requested by the electric motor-generator. The voltage drop across the battery is then calculated as (Eq. (5)): V ¼ VOC IRint
(5)
The battery performance, obtained with the above mentioned simulation model, were then compared with the experimental results, as shown in Figs. 5 and 6.
Fig. 3 e Vehicle speed (top), motor speed (middle) and motor torque (bottom) over NEDC.
The modelling of the vehicle is performed through a quasistatic approach: a driver model (PID controller) compares the target vehicle speed with the actual speed and generates a power demand profile to follow the target vehicle speed profile, by solving the longitudinal vehicle dynamics equation. However, although system dynamics is taken into account, the behaviour of the main devices (fuel cell, electric motorgenerator, batteries) is described using steady state performance maps [27]. The external load on the vehicle is calculated using the main vehicle characteristics and the vehicle resistance drag measured through the coast down test, as reported in Table 1. The electric motor speed and torque profiles along the NEDC and ASTERICS driving cycle are shown respectively in Figs. 3 and 4: good agreement between experimentally measured and calculated values can be observed, thus confirming a more than satisfactory model calibration. The battery is operated on the basis of its State of Charge (SOC). The SOC defines the level of capacity remaining in the battery. The SOC is calculated by the power being drawn from, or supplied to, the electric circuit, depending on the direction of the current I (Eqs. (1)e(3)): SOC ¼
Insta: Capacity Max: Capacity
(1)
Fig. 4 e Vehicle speed (top), motor speed (middle) and motor torque (bottom) over ASTERICS driving cycle.
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Positive currents indicate that the battery is supplying the electric motor-generator; instead negative currents indicate the motor-generator is charging the battery through the regenerative braking. The good agreement between the predicted and measured battery performance over both tested driving cycles indicates that the model is correctly capturing the battery charge and discharge characteristics, and is, therefore, capable of properly estimating the vehicle range in its BEV configuration.
Fuel cell model An electrochemical model of a PEM fuel cell consisting of open circuit voltage (theoretical maximum voltage) and over potential calculations was implemented. Considering the basic chemical reaction for the hydrogen/ oxygen fuel cell (Eq. (6)): 1 H2 þ O2 /H2 O 2
(6)
The open circuit voltage (VOC) of the cell can be written through the Gibbs free energy of formation of the reaction (Eq. (7)):
VOC
gf gf 0:5$ gf Dgf H2 O H2 O2 ¼ ¼ 2F 2F
(7)
Fig. 5 e Battery pack electric current (top), voltage (middle) and SOC (bottom) over NEDC.
5
where (ḡf)i is the Gibbs free energy of formation of specie i and F is the Faraday's constant. The fluid properties, such as enthalpy and entropy, are implemented in the model as a function of temperature and pressure. The losses that are being considered are: - Activation voltage loss: occurs at the start of chemical reactions, because part of the available energy is lost to move electrons and to break and form chemical bonds in the anode and cathode. These losses occur on both anode and cathode catalysts, but the oxygen reduction reaction kinetics at the cathode is much slower than hydrogen oxidation reaction at the anode, thus the voltage drop due to the activation loss is dominated by the cathode reaction conditions. The relation between the activation voltage loss and the current density can be described by the Tafel equation (Eq. (8)): Vact ¼
Rgas $T i $ln i0 2$a$F
(8)
The parameter a is the charge transfer coefficient, Rgas is the universal gas constant, T is the fuel cell operating temperature, F is the Faraday's constant, i is the fuel cell current density and i0 is the fuel cell exchange current density. - Ohmic voltage loss: is due to the resistance to the flow of electrons through the electrically conductive fuel cell
Fig. 6 e Battery pack electric current (top), voltage (middle) and SOC (bottom) over ASTERICS driving cycle.
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Fuel cell stack
Table 2 e Main fuel cell characteristics and operating conditions. Characteristics and operating conditions Number of cells Active surface area Anode pressure Cathode pressure Stoichiometry H2/Air FC Mass FC Thermal capacity
e cm2 bar bar e kg J/kgK
52 200 1.1 1 1.5/2.5 28 1250
components and to the flow of protons through the polymer membrane. The voltage drop is proportional to the current density (Eq. (9)): Vohm ¼ I$R
(9)
Thermal management of fuel cell
where R is the internal cell resistance. - Mass transport (concentration) voltage loss: occurs for the change in the concentration of the reactants, as they are consumed in the reaction (Eq. (10)). i Vmt ¼ C$ln 1 il
(10)
where C is mass transport loss coefficient and il is the limiting current density [28e30]. Finally, the fuel cell operating voltage is obtained by taking the difference between the open circuit voltage and the total voltage loss caused by the irreversibilities (Eq. (11)): Vcell ¼ VOC Vact Vohm Vmt
The fuel cell stack used has been developed during the ARTEMIS European project and consists of 52 cells with an active area of 200 cm2. The main fuel cell characteristics and operating conditions are summarized in Table 2. The rated output power of the fuel cell stack is 3 kW. The polarization curve at 160 C is shown in Fig. 7, where it is compared with the DPS G77, which was assumed as a reference benchmark. The temperature effect on some model parameters, e.g. charge transfer coefficient, exchange current density and internal ohmic resistance, is implemented into the model. The comparison of predicted and experimental polarization curves at 130 C and 160 C, of the fuel cell developed during Artemis project, is shown in Fig. 8.
(11)
The power request is the input of the fuel cell model, which defines a current density and an operating voltage of the stack. The fuel cell model can be easily tuned to correlate the simulated polarization curves with the experimental ones: the a, i0, il, C, R parameters are obtained through curve fitting on the experimental polarization curves.
Fig. 7 e Comparison between polarization curves of FC DPS G77 (reference) and Artemis project fuel cell.
High temperature PEM fuel cells operate at temperatures in the range of 120e180 C to avoid the presence of liquid water on the membranes. The fuel cell operating temperature depends on the fuel used and the required durability of the fuel cell. High fuel cell operating temperature improves the fuel cell tolerance to CO, but can accelerate the membrane degradation. Another issue to be addressed during the HT-PEMFC design is the start-up times, because of the high temperatures required for this type of fuel cells. A thermal model of the fuel cell has also been developed to capture the fuel cell behaviour during the warm-up phase. In Ref. [31] two different heating strategies are experimentally analysed: direct electrical heating and hot air heating. The experimental work showed that the hot air heating strategy is the faster and more efficient way to heat the fuel cell stack, ensuring, at the same time, a more uniform heat distribution in the stack. The start-up time of a thermal mass representative of a fuel cell is a function of the heat transfer, thermal losses and mass.
Fig. 8 e Polarization curves of Artemis project fuel cell at different operating temperatures.
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As can be seen in Fig. 9, the fuel cell stack takes about 10 min to reach the operating temperature of 110 C, if a 6 kW heater is used and the start temperature is equal to 10 C. After about 35 min, the cooling circuit starts to operate maintaining a constant temperature of 160 C.
Simulation results
Fig. 9 e Fuel cell temperature during the start-up.
t¼
ms cp;s DT Q_ in
(12)
Eq. (12) is used to calculate the time t for heating a mass ms by DT, with a specific heat capacity cp,s, neglecting the losses and assuming that all input energy Q_ in causes a temperature increase [31]. A fuel cell stack mass of 28 kg, with a thermal mass of 35 kJ K1 (including 10 kJ K1 for 5 L of cooling oil) has been considered. Three steps of operation have to be distinguished during the fuel cell warm-up: 1. Pre-heating (electrically) to 110 C to obtain the minimum temperature level for fuel cell operation. 2. Fuel cell operation while increasing the system temperature with waste heat from the fuel cell (pre-heater is off). 3. Constant fuel cell operation at 160 C with the removal of excess heat by means of the cooling system [32].
Fig. 10 e Model results for fuel cell range extension over NEDC. Fuel cell operating temperature of 160 C. Hydrogen tank of 30 L at 350 bar.
After the previously described model set-up and calibration, the benefits of the introduction of a FC-RE on the FIAT Iveco Daily 35S could be investigated through numerical simulation. The FC-RE is used to power the electrical loads of the vehicle, (also including the coolant pump, used for the fuel cell conditioning, and the air compressor used to ensure adequate air flow to the fuel cell): the total electric load supplied by the fuel cell is about 1.3 kW. As far as the vehicle operating conditions are concerned, an average vehicle weight, between the curb weight and the full load weight, was considered, assuming that the delivery van is full at the start of its daily mission and empty at the end. Fig. 10 shows the model results over the NEDC driving cycle: the driving cycle is repeated until the battery SOC drops to a minimum value of 20%. Fig. 10 shows that when the FC-RE provides 1.3 kW of electrical power to supply the accessory loads, the vehicle runtime is improved of about 20 min respect to the full electric vehicle. In the first phase of the NEDC (first 600s), the FC-RE is not operating because it is below the minimum temperature for operation (110 C). In this condition, the battery supplies 6 kW of additional power to electrically pre-heat the fuel cell stack, thus leading to a dramatic discharge rate. The simulations were performed with a hydrogen tank capacity of 30 L, with a maximum pressure of 350 bar. Afterwards, a sensitivity analysis was carried out to assess the impact on the hydrogen consumption of an enhanced polarization curve. In Fig. 11 the simulation results over the ASTERICS mission profile, which is more representative of the real world driving conditions, are shown.
Fig. 11 e Model results for fuel cell range extension over Asterics driving cycle. Fuel cell operating temperature of 160 C. Hydrogen tank of 30 L at 350 bar.
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Fig. 12 e Comparison between FEV and FC-REEV ranges (80% of SOC swing).
Fig. 12 shows the effects of the introduction of the FC-RE on the vehicle range: an 11% increase in the vehicle range can be observed for the NEDC mission profile, while a 19% improvement can be noticed for the ASTERICS mission profile. Andaloro et al. found out in their research that a 5 kW fuel cell is able to increase the range of an electric bus of about 40% on a real urban load profile [17]. Considering the larger size of the fuel cell, this result is comparable with that achieved on the Iveco Daily 35S. Fuel cell technology, in particular HT-PEMFC, is suitable for the automotive applications thanks to its high energy and power density. Energy and power density of battery and fuel cell are reported in Table 3. The mass of the fuel cell system was estimated considering both fuel cell and hydrogen tank mass. The hydrogen tank mass was calculated considering the weight of 30 L of hydrogen at 350 bar (about 0.773 kg) and the U.S. Department of Energy (DOE) target 5.5% of system gravimetric capacity [33]. The specific ranges of FEV and FC-REEV, calculated according Eq. (13), are compared in Fig. 13. specific range ¼
vehicle range energy storage mass
(13)
As shown in Fig. 13, the usage of the fuel cell as a range extender is more advantageous, from the weight point of view, respect to the battery capacity increase. This is mainly due to the higher energy density of the fuel cell system compared to the batteries. The fuel cell voltage, efficiency, current density and hydrogen consumption are presented in Fig. 14. As it can be observed, the fuel cell voltage increases with the temperature due to the enhanced electrochemical kinetics and the
Table 3 e Energy and power density comparison between ZEBRA batteries and Artemis Fuel Cell (hydrogen tank of 30 L at 350 bar).
Mass [kg] Energy density [Wh/kg] Power density [W/kg]
ZEBRA® batteries [20]
Artemis FC þ hydrogen tank
360 120 180
42 (28 þ 14) 210 71
Fig. 13 e Specific range of FEV and FC-REEV.
reduction of the membrane resistance to the proton flow. Because the increased voltage, the current density decreases to keep the fuel cell power output constant. This reduction in current density decreases the hydrogen consumption making the fuel cell work at a higher efficiency.
Hydrogen storage capacity analysis The analysis described in the previous section highlights the possibility of resizing the hydrogen tank volume to ensure that all the hydrogen is consumed when the battery reaches the minimum allowed SOC (20%). The optimal hydrogen tank capacity depends on the driving profile and the characteristics of the fuel cell, as shown in Fig. 15. The NEDC driving cycle, which is characterized by a much deeper battery discharge, because of the higher vehicle speeds during the extra-urban phase, presents a vehicle runtime much lower respect to the ASTERICS driving cycle, thus requiring a lower capacity of the hydrogen tank. Moreover, the usage of a high efficiency fuel cell, such as the one developed in the framework of the ARTEMIS project, can lead to a decrease in the hydrogen consumption, and, as a consequence, of the hydrogen tank capacity.
Conclusions In this work, the benefits of using a High Temperature PEM Fuel Cell on-board of a Full Electric Vehicle as a range extender were analysed. Through the use of a validated vehicle and fuel cell model, the range extension capability of a high-efficiency HT-PEMFC developed in the framework of the ARTEMIS European project was assessed. The fuel cell characteristics have been implemented through a fitting of experimental polarization curves, and a transient thermal model of the fuel cell, including heating and cooling control strategies, has been created. Furthermore, the minimum hydrogen tank volume capable of ensuring the complete range extension during two different driving cycles (NEDC and ASTERICS) was evaluated. This analysis demonstrated that the usage of a fuel cell to supply 1.3 kW of accessory loads increases the vehicle range (or equivalently the runtime) of 11% over the European type approval driving cycle (NEDC) and of 19% over a real world
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Fig. 14 e Fuel cell operating condition during start-up.
Improved meas and Stacks, grant number 303482) is gratefully acknowledged, as well as the support of the project partners: CNRS, CEA, Nedstack, Cidetec.
references
Fig. 15 e Minimum hydrogen tank volume capacity for different driving mission profiles and fuel cells.
urban driving cycle (ASTERICS). These results are obtained assuming a hydrogen tank capacity of 30 L, with a maximum pressure of 350 bar. The fuel cell technology for range extension is also convenient regarding the weight, because of the higher energy density of the fuel cell system compared to the battery. Moreover, the analysis of two different fuel cells showed a 5% decrease in hydrogen consumption passing from the state-of-the-art fuel cell to the improved one, thanks to its higher conversion efficiency.
Acknowledgements The financial support of the European project ARTEMIS (Automotive pemfc Range extender with high TEMperature
[1] Eurostat, Statistics Explained. Climate change - driving forces. http://ec.europa.eu/eurostat/statistics-explained/ index.php/Climate_change_-_driving_forces [accessed 25.09.15]. [2] Manzetti S, Mariasiu F. Electric vehicle battery technologies: from present state to future systems. Renew Sustain Energy Rev 2015;51:1004e12. [3] Smith WJ. Can EV (electric vehicles) address Ireland's CO2 emissions from transport? Energy 2010;35:4514e21. [4] Ku¨hne R. Electric buses e an energy efficient urban transportation means. Energy 2010;35:4510e3. [5] Schneidereit T, Franke T, Gu¨nther M, Krems JF. Does range matter? Exploring perceptions of electric vehicles with and without a range extender among potential early adopters in Germany. ERSS 2015;8:198e206. [6] Andreasen SJ, Ashworth L, Sahlin S, Jensen HCB, Kær SK. Test of hybrid power system for electrical vehicles using a lithium-ion battery pack and a reformed methanol fuel cell range extender. Int J Hydrogen Energy 2014;39:1856e63. Y. Enhanced fuel [7] Maalej M, Kelouwani S, Agbossou K, Dube cell hybrid electric vehicle power sharing method based on fuel cost and mass estimation. J Power Sources 2014;248:668e78. [8] Hwang JJ, Hu JS, Lin CH. Design of a range extension strategy for power decentralized fuel cell/battery electric vehicles. Int J Hydrogen Energy 2015;40:11704e12. [9] Casolari BL, Ellington MA, Oros JM, Schuttinger P, Radley CJ, Kiley KA, et al. Model study of a fuel cell range extender for a
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
10
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23] [24] [25]
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neighborhood electric vehicle (NEV). Int J Hydrogen Energy 2014;39:10757e87. Sergi F, Andaloro L, Napoli G, Randazzo N, Antonucci V. Development and realization of a hydrogen range extender hybrid city bus. J Power Sources 2014;250:286e95. Cordner M, Matian M, Offer GJ, Hanten T, Spofforth-Jones E, Tippetts S, et al. Designing, building, testing and racing a low-cost fuel cell range extender for a motorsport application. J Power Sources 2010;195:7838e48. Sharer P, Rousseau A. Benefit of fuel cell range extender for medium-duty vehicle applications. In: EVS27 Electric Vehicle Symposium and Exhibition, Barcelona Spain; 2013. Sapienza C, Andaloro L, Matera FV, Dispenza G, Cretı` P, Ferraro M, et al. Batteries analysis for FC-hybrid powertrain optimization. Int J Hydrogen Energy 2008;33:3230e4. De Lorenzo G, Andaloro L, Sergi F, Napoli G, Ferraro M, Antonucci V. Numerical simulation model for the preliminary design of hybrid electric city bus power train with polymer electrolyte fuel cell. Int J Hydrogen Energy 2014;39:12934e47. n Remo n IN, Kær SK. Andreasen SJ, Ashworth L, Menjo Directly connected series coupled HTPEM fuel cell stacks to a Li-ion battery DC bus for a fuel cell electrical vehicle. Int J Hydrogen Energy 2008;33:7137e45. Le Duigou A, Smatti A. On the comparison and the complementarity of batteries and fuel cells for electric driving. Int J Hydrogen Energy 2014;39:17873e83. Andaloro L, Napoli G, Sergi F, Dispenza G, Antonucci V. Design of a hybrid electric fuel cell power train for an urban bus. Int J Hydrogen Energy 2013;38:7725e32. Corbo P, Migliardini F, Veneri O. PEFC stacks as power sources for hybrid propulsion systems. Int J Hydrogen Energy 2009;34:4635e44. Carton JG, Lawlor V, Olabi AG, Hochenauer C, Zauner G. Water droplet accumulation and motion in PEM (Proton Exchange Membrane) fuel cell mini-channels. Energy 2012;39:63e73. Salomov UR, Chiavazzo E, Asinari P. Pore-scale modeling of fluid flow through gas diffusion and catalyst layers for high temperature proton exchange membrane (HT-PEM) fuel. Comput Math Appl 2014;67:393e411. Salomov UR, Chiavazzo E, Asinari P. Gas-dynamic and electro-chemical optimization of catalyst layers in high temperature polymeric electrolyte membrane fuel cells. Int J Hydrogen Energy 2015;40:5425e31. Janßen H, Supra J, Lu¨ke L, Lehnert W, Stolten D. Development of HT-PEFC stacks in the kW range. Int J Hydrogen Energy 2013;38:4705e13. Dustmann C. Advances in ZEBRA batteries. J Power Sources 2004;127:85e92. GT-SUITE. Vehicle driveline and HEV application manual. Gamma Technologies; 2015. Wahiduzzaman S, Kolade B, Buyuktur S. An integrated proton exchange membrane fuel cell vehicle model. Detroit Michigan: SAE World Congress; 2004.
[26] ASTERICS project homepage www.asterics-project.eu/ mainmenu/home.html [accessed 05.07.15]. [27] Millo F, Rolando L, Andreata M. Numerical simulation for vehicle powertrain development. Rijeka: InTech Numer Analysis - Theory Appl 2011:519e40. [28] Husar A, Strahl S, Riera J. Experimental characterization methodology for the identification of voltage losses of PEMFC: applied to an open cathode stack. Int J Hydrogen Energy 2012;37:7309e15. [29] Pukrushpan JT, Stefanopoulou AG, Peng H. Control of fuel cell power systems. Fuel cell system model: fuel cell stack. London: Springer-Verlag; 2004. p. 31e56. [30] Zhang X, Guo J, Chen J. The parametric optimum analysis of a proton exchange membrane (PEM) fuel cell and its load matching. Energy 2010;35:5294e9. [31] Andreasen SJ, Kær SK. Modelling and evaluation of heating strategies for high temperature polymer electrolyte membrane fuel cell stacks. Int J Hydrogen Energy 2008;33:4655e64. [32] Nasri M, Dickinson D. Thermal management of fuel celldriven vehicles using HT-PEM and hydrogen storage. In: Ninth International Conference on Ecological Vehicles and Renewable Energies (EVER), Monaco; 2014. [33] Argonne National Laboratory. Technical assessment of compressed hydrogen storage tank systems for automotive applications. https://www1.eere.energy.gov/ hydrogenandfuelcells/pdfs/compressedtank_storage.pdf [accessed 17.03.16].
Nomenclature BEV: Battery Electric Vehicle FC: Fuel Cell FCEV: Fuel Cell Electric Vehicle FC-RE: Fuel Cell e Range Extender FC-REEV: Fuel Cell e Range Extended Electric Vehicle FEV: Full Electric Vehicle GHG: Greenhouse Gas HEV: Hybrid Electric Vehicle HT-PEMFC: High Temperature e Proton Exchange Membrane Fuel Cell ICE: Internal Combustion Engine ICE-RE: Internal Combustion Engine e Range Extender LD: Light Duty LD-FEV: Light Duty e Full Electric Vehicle NEDC: New European Driving Cycle OCV: Open Circuit Voltage OEM: Original Equipment Manufacturer RE: Range Extender SOC: State Of Charge ZEBRA®: Zero Emission Battery Research Activities ZEV: Zero Emissions Vehicle
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV) F. Millo a,*, S. Caputo a, A. Piu b a b
Energy Department, Politecnico di Torino, Italy Centro Ricerche Fiat (C.R.F), Turin, Italy
article info
abstract
Article history:
The usage of a Fuel Cell (FC) as a range extender in a Full Electric Vehicle (FEV) is a
Received 16 November 2015
convenient solution to address the issue of the shortage of range of this type of vehicles.
Received in revised form
Compared with the Internal Combustion Engine e Range Extender (ICE-RE), the Fuel Cell e
18 April 2016
Range Extender (FC-RE) has the potential to provide power with higher efficiency (more
Accepted 18 April 2016
than 50%) and, above all, it can allow zero emissions operation of the vehicle even when
Available online xxx
the on-board power source is switched on for range extension.
Keywords:
Membrane Fuel Cell), developed in the framework of the collaborative European project
HT-PEM fuel cell
ARTEMIS (Automotive pemfc Range extender with high TEMperature Improved meas and
Range extender
Stacks), on a light duty, full electric, commercial vehicle, was investigated.
In this work, the introduction of a new HT-PEMFC (High TemperatureeProton Exchange
Battery
Firstly, a model of the Full Electric Vehicle was created and validated by means of
Electric vehicle
experimental tests carried out on rolling chassis dyno over both type approval and real
Fuel cell vehicle
world driving cycles. Once the model was developed, the effects of the introduction of an HT-PEMFC on the vehicle range was evaluated and the performances of different HT-PEM fuel cell stack systems, combined with various hydrogen storage system configurations, were compared. © 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction With a share of more than 20% of total greenhouse gasses in 2009, transport is the only source of emissions in the EU which has exhibited continuously growing in the decade 2000e2009. Besides GHG emissions, transport is also responsible for other negative externalities, e.g. air pollution and particulate matters, due to the oil-derived fuels used in the internal combustion engines.
For these reasons, the EU Sustainable Development Strategy is addressed to a balanced shift towards environmentally friendly transport modes, including the development of zero/ low emissions vehicles [1]. The usage of electric energy for powering the land vehicles represents a key step towards the reduction of the greenhouse gas and pollutant emissions. Battery Electric Vehicles (BEVs), that use a battery stack for power an electric motor, are becoming an attractive solution for Europe and US automotive markets. The BEV powertrains give the possibility to operate
* Corresponding author. E-mail addresses: [email protected] (F. Millo), [email protected] (S. Caputo), [email protected] (A. Piu). http://dx.doi.org/10.1016/j.ijhydene.2016.04.120 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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with zero emissions in the place of use (zero tank-to-wheel emissions). The advantages of using BEV are the high overall energy efficiency, thanks to energy recovery capability (e.g. regenerative braking), and the higher torque transmitted to the wheels compared to a traditional vehicle equipped with an Internal Combustion Engine (ICE). Furthermore, BEVs do not produce noise and pollutant emissions. These characteristics make them the ideal vehicles to be used in the urban areas [2,3]. Battery Electric Vehicles are also the best solution for usages that do not require long-range daily driving, as the delivery vans and city buses. Ku¨hne described in his work how the electric buses can solve energy, pollution and urban traffic problems [4]. However, pure Battery Electric Vehicles (BEVs) raise several problems that have to be overcome to make them competitive on the market, such as cost, weight, short driving range, long charging time, limited lifespan, etc. Range Extenders (REs) are one mean to enhance the driving range of BEVs using an electricity-generating equipment onto the vehicle that completes the battery energy. Nowadays, the use of Internal Combustion Engines (ICEs) as range extenders is the most exploited solution by car makers. The Internal Combustion Engine e Range Extender (ICE-RE) assists the battery's State Of Charge (SOC) in maintaining a higher level, extending the vehicle range and the overall battery life. Unfortunately, when the ICE-RE is in operation, the vehicle is not in a pollution-free mode, and, so, does not fulfil the requirements of a Zero Emissions Vehicle (ZEV) [5]. The Fuel Cell - Range Extended Electric Vehicle (FC-REEV) is a possible solution to improve the battery range maintaining zero tank-to-wheel emissions capability [6e8]. Several studies have examined the range extension of Full Electric Vehicles (FEVs) through the use of fuel cell stacks [6e15]. Le Duigou and Smatti [16] compared different powertrain technologies (ICE, BEV, HEV, FCEV and FC-RE) within a techno-economic framework. If vehicles totally based on fuel cell are still showing difficulties in the market penetration, especially for the high cost, the hybridization of fuel cell with other technologies (e.g. batteries) can reduce the life-cycle cost of vehicles, facilitating their market introduction. Moreover, the quantity of hydrogen carried on board the FC-REEV is quite low, allowing fast refuelling and low hydrogen tank weight. Besides, a small FC used as a range extender allows to reduce capacity, weight and recharging time of batteries, ensuring the same range of an equivalent BEV. In order to fully exploit the advantages of FC-REEVs, an energy analysis must be carefully performed, planning some strategies of energy management to optimize the total efficiency and safeguard the devices from excessive stress that can limit their lifecycle [17]. Corbo et al. [18] performed an experimental analysis with the scope to investigate the energy management issues of two electric hybrid powertrains for scooter and minibus applications. The experiments they have carried out on the two hybrid powertrains showed that the overall efficiency is not significantly influenced by the hybrid configuration adopted, as the efficiency values ranged from 27 to 29% in the different cases analysed. This is due to the negligible influence of load
on the fuel cell efficiency, which is the main difference with respect to an internal combustion engine. In this work, the introduction of a new High TemperatureeProton Exchange Membrane Fuel Cell (HT-PEMFC), developed in the framework of the collaborative European project ARTEMIS (Automotive pemfc Range extender with high TEMperature Improved meas and Stacks), to extend the range of a Light Duty e Full Electric Vehicle (LD-FEV), the FIAT Iveco Daily 35S, was analysed. Proton Exchange Membrane Fuel Cells (PEMFCs) offer many advantages including high power density, rapid start-up and high efficiency. The HT-PEM is assembled with phosphoric acid doped poly-benzimidazole (PBI) membranes and works between 120 C and 180 C. Unlike low temperature PEM fuel cells, HT-PEM fuel cells need no humidification and, therefore, eliminates water management issues [19]. Moreover, they are characterized by enhanced electrochemical kinetics and higher carbon monoxide tolerance. For these reasons, HT-PEM stacks can be the most suitable PEM technology for a transportation range extender [20,21]. Janben et al. [22] investigated about the performance of a high temperature polymer electrolyte fuel cell stack varying some operating parameters, as anode and cathode stoichiometry's, temperature and fuel used (pure hydrogen or synthetic reformate). In order to assess the advantages of a fuel cell range extension, a numerical model of the FIAT Iveco Daily 35S was created and validated by means of experimental tests, carried out on rolling chassis dyno at Centro Ricerche Fiat (C.R.F). The calculation tool was then used to examine the effects of the introduction of a fuel cell, which supplies the accessory loads (pumps, radiator fan, lights, cabin heater, etc.), on the vehicle range, assuming that the existing battery package is maintained and used to provide power to the electric motor. Furthermore, the benefits deriving from the usage of the new, high performance HT-PEMFC, developed in the ARTEMIS project, were assessed.
Powertrain configuration As above said, in order to test the concept of using an HTPEMFC as a range extender in an electrical, automotive application, the FIAT Iveco Daily 35S is chosen as a case study (Fig. 1). In Table 1 the technical characteristics of the vehicle are reported. The powertrain is driven by an asynchronous three phase electric motor, featuring a 30 kW nominal power (60 kW peak power) and supplied from an inverter via 2 ZEBRA® (Zero Emission Battery Research Activities) batteries. The motor is directly responsible for moving the vehicle and recovering energy while braking. In Fig. 2, a schematic of the battery electric system is shown. The battery electric system is characterized by two traction batteries (ZEBRA), used to supply the electric traction motor through an inverter and the hydro-steering pump, and a low voltage battery (12 V), used to supplies the other accessory loads, as radiator fan, water and vacuum pumps. High and low voltage lines are connected through two DC/DC converters.
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Battery pack
Fig. 1 e FIAT Iveco Daily 35S.
Table 1 e Technical characteristics of the FIAT Iveco Daily 35S.
The battery pack is composed of 2 ZEBRA® batteries (Model Z5278-ML3P-76, Rated Capacity: 76 Ah, Rated Energy: 21.2 kWh, OCV: 278 V). ZEBRA® batteries, with a specific energy of ca. 120 Wh/kg and a specific power of ca. 180 W/kg, is a good solution for mobile applications like cars, vans and buses. In the charged state, the ZEBRA® cell has a positive electrode consisting of nickel chloride and a negative electrode composed of sodium. During the discharging phase, the sodium reacts with the nickel chloride to form sodium chloride and nickel. The process takes place in the reverse direction during the charging phase. A liquid electrolyte consisting of “b” alumina is used to conduct sodium ions and to ensure the electrical insulation between anode and cathode. This sodium-ion conductivity is higher at temperature not lower than 260 C, therefore, the operational temperature of ZEBRA® batteries is in the range of 270e350 C. A second electrolyte in molten state (sodium aluminium chloride) provides the ion conducting properties inside the positive electrode [23].
Technical characteristics Vehicle characteristics
Curb Weight Full Load Weight Drag force @100kph Maximum speed Motor e generator Electric motor characteristics Nominal power Peak power Battery Batteries characteristics Battery voltage (OCV) Battery capacity Rated energy
kg kg N km/h Type kW kW Type V Ah kWh
2500 3500 1270 70 Asynchronousthree-phase 30 60 2 ZEBRA® Z5-278-ML3P-76 278 76 21.2
FEV model development The vehicle model was created with GT-SUITE, a commercially available modelling tool developed by Gamma Technologies, which allows the assessment of the vehicle performance along a driving cycle [24,25]. The model was then validated with experimental data gathered both along the European type approval driving cycle (New European Driving Cycle, NEDC) and along a real world driving cycle developed by the OEMs in the framework of the European collaborative project ASTERICS [26].
Fig. 2 e Schematic of the battery electrical system. Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
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Z Insta: Capacity ¼ Q0
Idt
(2)
t
Q0 ¼ SOC0 $Maximum Capacity
(3)
where Q0 is the initial battery charge, I is the instantaneous current and SOC0 is the initial value of the SOC. The battery model in this simulation study is simplified as an equivalent circuit with a voltage source and a resistance (Eq. (4)): IVOC I2 Rint C$Prequest ¼ 0
(4)
where I is the instantaneous current, VOC is the Open Circuit Voltage (increasing with the battery SOC), Rint is the internal resistance of the battery (decreasing with battery SOC), C is its Coulombic efficiency, normally applied when the battery is charging (C > 1) and Prequest is the power requested by the electric motor-generator. The voltage drop across the battery is then calculated as (Eq. (5)): V ¼ VOC IRint
(5)
The battery performance, obtained with the above mentioned simulation model, were then compared with the experimental results, as shown in Figs. 5 and 6.
Fig. 3 e Vehicle speed (top), motor speed (middle) and motor torque (bottom) over NEDC.
The modelling of the vehicle is performed through a quasistatic approach: a driver model (PID controller) compares the target vehicle speed with the actual speed and generates a power demand profile to follow the target vehicle speed profile, by solving the longitudinal vehicle dynamics equation. However, although system dynamics is taken into account, the behaviour of the main devices (fuel cell, electric motorgenerator, batteries) is described using steady state performance maps [27]. The external load on the vehicle is calculated using the main vehicle characteristics and the vehicle resistance drag measured through the coast down test, as reported in Table 1. The electric motor speed and torque profiles along the NEDC and ASTERICS driving cycle are shown respectively in Figs. 3 and 4: good agreement between experimentally measured and calculated values can be observed, thus confirming a more than satisfactory model calibration. The battery is operated on the basis of its State of Charge (SOC). The SOC defines the level of capacity remaining in the battery. The SOC is calculated by the power being drawn from, or supplied to, the electric circuit, depending on the direction of the current I (Eqs. (1)e(3)): SOC ¼
Insta: Capacity Max: Capacity
(1)
Fig. 4 e Vehicle speed (top), motor speed (middle) and motor torque (bottom) over ASTERICS driving cycle.
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Positive currents indicate that the battery is supplying the electric motor-generator; instead negative currents indicate the motor-generator is charging the battery through the regenerative braking. The good agreement between the predicted and measured battery performance over both tested driving cycles indicates that the model is correctly capturing the battery charge and discharge characteristics, and is, therefore, capable of properly estimating the vehicle range in its BEV configuration.
Fuel cell model An electrochemical model of a PEM fuel cell consisting of open circuit voltage (theoretical maximum voltage) and over potential calculations was implemented. Considering the basic chemical reaction for the hydrogen/ oxygen fuel cell (Eq. (6)): 1 H2 þ O2 /H2 O 2
(6)
The open circuit voltage (VOC) of the cell can be written through the Gibbs free energy of formation of the reaction (Eq. (7)):
VOC
gf gf 0:5$ gf Dgf H2 O H2 O2 ¼ ¼ 2F 2F
(7)
Fig. 5 e Battery pack electric current (top), voltage (middle) and SOC (bottom) over NEDC.
5
where (ḡf)i is the Gibbs free energy of formation of specie i and F is the Faraday's constant. The fluid properties, such as enthalpy and entropy, are implemented in the model as a function of temperature and pressure. The losses that are being considered are: - Activation voltage loss: occurs at the start of chemical reactions, because part of the available energy is lost to move electrons and to break and form chemical bonds in the anode and cathode. These losses occur on both anode and cathode catalysts, but the oxygen reduction reaction kinetics at the cathode is much slower than hydrogen oxidation reaction at the anode, thus the voltage drop due to the activation loss is dominated by the cathode reaction conditions. The relation between the activation voltage loss and the current density can be described by the Tafel equation (Eq. (8)): Vact ¼
Rgas $T i $ln i0 2$a$F
(8)
The parameter a is the charge transfer coefficient, Rgas is the universal gas constant, T is the fuel cell operating temperature, F is the Faraday's constant, i is the fuel cell current density and i0 is the fuel cell exchange current density. - Ohmic voltage loss: is due to the resistance to the flow of electrons through the electrically conductive fuel cell
Fig. 6 e Battery pack electric current (top), voltage (middle) and SOC (bottom) over ASTERICS driving cycle.
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Fuel cell stack
Table 2 e Main fuel cell characteristics and operating conditions. Characteristics and operating conditions Number of cells Active surface area Anode pressure Cathode pressure Stoichiometry H2/Air FC Mass FC Thermal capacity
e cm2 bar bar e kg J/kgK
52 200 1.1 1 1.5/2.5 28 1250
components and to the flow of protons through the polymer membrane. The voltage drop is proportional to the current density (Eq. (9)): Vohm ¼ I$R
(9)
Thermal management of fuel cell
where R is the internal cell resistance. - Mass transport (concentration) voltage loss: occurs for the change in the concentration of the reactants, as they are consumed in the reaction (Eq. (10)). i Vmt ¼ C$ln 1 il
(10)
where C is mass transport loss coefficient and il is the limiting current density [28e30]. Finally, the fuel cell operating voltage is obtained by taking the difference between the open circuit voltage and the total voltage loss caused by the irreversibilities (Eq. (11)): Vcell ¼ VOC Vact Vohm Vmt
The fuel cell stack used has been developed during the ARTEMIS European project and consists of 52 cells with an active area of 200 cm2. The main fuel cell characteristics and operating conditions are summarized in Table 2. The rated output power of the fuel cell stack is 3 kW. The polarization curve at 160 C is shown in Fig. 7, where it is compared with the DPS G77, which was assumed as a reference benchmark. The temperature effect on some model parameters, e.g. charge transfer coefficient, exchange current density and internal ohmic resistance, is implemented into the model. The comparison of predicted and experimental polarization curves at 130 C and 160 C, of the fuel cell developed during Artemis project, is shown in Fig. 8.
(11)
The power request is the input of the fuel cell model, which defines a current density and an operating voltage of the stack. The fuel cell model can be easily tuned to correlate the simulated polarization curves with the experimental ones: the a, i0, il, C, R parameters are obtained through curve fitting on the experimental polarization curves.
Fig. 7 e Comparison between polarization curves of FC DPS G77 (reference) and Artemis project fuel cell.
High temperature PEM fuel cells operate at temperatures in the range of 120e180 C to avoid the presence of liquid water on the membranes. The fuel cell operating temperature depends on the fuel used and the required durability of the fuel cell. High fuel cell operating temperature improves the fuel cell tolerance to CO, but can accelerate the membrane degradation. Another issue to be addressed during the HT-PEMFC design is the start-up times, because of the high temperatures required for this type of fuel cells. A thermal model of the fuel cell has also been developed to capture the fuel cell behaviour during the warm-up phase. In Ref. [31] two different heating strategies are experimentally analysed: direct electrical heating and hot air heating. The experimental work showed that the hot air heating strategy is the faster and more efficient way to heat the fuel cell stack, ensuring, at the same time, a more uniform heat distribution in the stack. The start-up time of a thermal mass representative of a fuel cell is a function of the heat transfer, thermal losses and mass.
Fig. 8 e Polarization curves of Artemis project fuel cell at different operating temperatures.
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As can be seen in Fig. 9, the fuel cell stack takes about 10 min to reach the operating temperature of 110 C, if a 6 kW heater is used and the start temperature is equal to 10 C. After about 35 min, the cooling circuit starts to operate maintaining a constant temperature of 160 C.
Simulation results
Fig. 9 e Fuel cell temperature during the start-up.
t¼
ms cp;s DT Q_ in
(12)
Eq. (12) is used to calculate the time t for heating a mass ms by DT, with a specific heat capacity cp,s, neglecting the losses and assuming that all input energy Q_ in causes a temperature increase [31]. A fuel cell stack mass of 28 kg, with a thermal mass of 35 kJ K1 (including 10 kJ K1 for 5 L of cooling oil) has been considered. Three steps of operation have to be distinguished during the fuel cell warm-up: 1. Pre-heating (electrically) to 110 C to obtain the minimum temperature level for fuel cell operation. 2. Fuel cell operation while increasing the system temperature with waste heat from the fuel cell (pre-heater is off). 3. Constant fuel cell operation at 160 C with the removal of excess heat by means of the cooling system [32].
Fig. 10 e Model results for fuel cell range extension over NEDC. Fuel cell operating temperature of 160 C. Hydrogen tank of 30 L at 350 bar.
After the previously described model set-up and calibration, the benefits of the introduction of a FC-RE on the FIAT Iveco Daily 35S could be investigated through numerical simulation. The FC-RE is used to power the electrical loads of the vehicle, (also including the coolant pump, used for the fuel cell conditioning, and the air compressor used to ensure adequate air flow to the fuel cell): the total electric load supplied by the fuel cell is about 1.3 kW. As far as the vehicle operating conditions are concerned, an average vehicle weight, between the curb weight and the full load weight, was considered, assuming that the delivery van is full at the start of its daily mission and empty at the end. Fig. 10 shows the model results over the NEDC driving cycle: the driving cycle is repeated until the battery SOC drops to a minimum value of 20%. Fig. 10 shows that when the FC-RE provides 1.3 kW of electrical power to supply the accessory loads, the vehicle runtime is improved of about 20 min respect to the full electric vehicle. In the first phase of the NEDC (first 600s), the FC-RE is not operating because it is below the minimum temperature for operation (110 C). In this condition, the battery supplies 6 kW of additional power to electrically pre-heat the fuel cell stack, thus leading to a dramatic discharge rate. The simulations were performed with a hydrogen tank capacity of 30 L, with a maximum pressure of 350 bar. Afterwards, a sensitivity analysis was carried out to assess the impact on the hydrogen consumption of an enhanced polarization curve. In Fig. 11 the simulation results over the ASTERICS mission profile, which is more representative of the real world driving conditions, are shown.
Fig. 11 e Model results for fuel cell range extension over Asterics driving cycle. Fuel cell operating temperature of 160 C. Hydrogen tank of 30 L at 350 bar.
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Fig. 12 e Comparison between FEV and FC-REEV ranges (80% of SOC swing).
Fig. 12 shows the effects of the introduction of the FC-RE on the vehicle range: an 11% increase in the vehicle range can be observed for the NEDC mission profile, while a 19% improvement can be noticed for the ASTERICS mission profile. Andaloro et al. found out in their research that a 5 kW fuel cell is able to increase the range of an electric bus of about 40% on a real urban load profile [17]. Considering the larger size of the fuel cell, this result is comparable with that achieved on the Iveco Daily 35S. Fuel cell technology, in particular HT-PEMFC, is suitable for the automotive applications thanks to its high energy and power density. Energy and power density of battery and fuel cell are reported in Table 3. The mass of the fuel cell system was estimated considering both fuel cell and hydrogen tank mass. The hydrogen tank mass was calculated considering the weight of 30 L of hydrogen at 350 bar (about 0.773 kg) and the U.S. Department of Energy (DOE) target 5.5% of system gravimetric capacity [33]. The specific ranges of FEV and FC-REEV, calculated according Eq. (13), are compared in Fig. 13. specific range ¼
vehicle range energy storage mass
(13)
As shown in Fig. 13, the usage of the fuel cell as a range extender is more advantageous, from the weight point of view, respect to the battery capacity increase. This is mainly due to the higher energy density of the fuel cell system compared to the batteries. The fuel cell voltage, efficiency, current density and hydrogen consumption are presented in Fig. 14. As it can be observed, the fuel cell voltage increases with the temperature due to the enhanced electrochemical kinetics and the
Table 3 e Energy and power density comparison between ZEBRA batteries and Artemis Fuel Cell (hydrogen tank of 30 L at 350 bar).
Mass [kg] Energy density [Wh/kg] Power density [W/kg]
ZEBRA® batteries [20]
Artemis FC þ hydrogen tank
360 120 180
42 (28 þ 14) 210 71
Fig. 13 e Specific range of FEV and FC-REEV.
reduction of the membrane resistance to the proton flow. Because the increased voltage, the current density decreases to keep the fuel cell power output constant. This reduction in current density decreases the hydrogen consumption making the fuel cell work at a higher efficiency.
Hydrogen storage capacity analysis The analysis described in the previous section highlights the possibility of resizing the hydrogen tank volume to ensure that all the hydrogen is consumed when the battery reaches the minimum allowed SOC (20%). The optimal hydrogen tank capacity depends on the driving profile and the characteristics of the fuel cell, as shown in Fig. 15. The NEDC driving cycle, which is characterized by a much deeper battery discharge, because of the higher vehicle speeds during the extra-urban phase, presents a vehicle runtime much lower respect to the ASTERICS driving cycle, thus requiring a lower capacity of the hydrogen tank. Moreover, the usage of a high efficiency fuel cell, such as the one developed in the framework of the ARTEMIS project, can lead to a decrease in the hydrogen consumption, and, as a consequence, of the hydrogen tank capacity.
Conclusions In this work, the benefits of using a High Temperature PEM Fuel Cell on-board of a Full Electric Vehicle as a range extender were analysed. Through the use of a validated vehicle and fuel cell model, the range extension capability of a high-efficiency HT-PEMFC developed in the framework of the ARTEMIS European project was assessed. The fuel cell characteristics have been implemented through a fitting of experimental polarization curves, and a transient thermal model of the fuel cell, including heating and cooling control strategies, has been created. Furthermore, the minimum hydrogen tank volume capable of ensuring the complete range extension during two different driving cycles (NEDC and ASTERICS) was evaluated. This analysis demonstrated that the usage of a fuel cell to supply 1.3 kW of accessory loads increases the vehicle range (or equivalently the runtime) of 11% over the European type approval driving cycle (NEDC) and of 19% over a real world
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0
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Fig. 14 e Fuel cell operating condition during start-up.
Improved meas and Stacks, grant number 303482) is gratefully acknowledged, as well as the support of the project partners: CNRS, CEA, Nedstack, Cidetec.
references
Fig. 15 e Minimum hydrogen tank volume capacity for different driving mission profiles and fuel cells.
urban driving cycle (ASTERICS). These results are obtained assuming a hydrogen tank capacity of 30 L, with a maximum pressure of 350 bar. The fuel cell technology for range extension is also convenient regarding the weight, because of the higher energy density of the fuel cell system compared to the battery. Moreover, the analysis of two different fuel cells showed a 5% decrease in hydrogen consumption passing from the state-of-the-art fuel cell to the improved one, thanks to its higher conversion efficiency.
Acknowledgements The financial support of the European project ARTEMIS (Automotive pemfc Range extender with high TEMperature
[1] Eurostat, Statistics Explained. Climate change - driving forces. http://ec.europa.eu/eurostat/statistics-explained/ index.php/Climate_change_-_driving_forces [accessed 25.09.15]. [2] Manzetti S, Mariasiu F. Electric vehicle battery technologies: from present state to future systems. Renew Sustain Energy Rev 2015;51:1004e12. [3] Smith WJ. Can EV (electric vehicles) address Ireland's CO2 emissions from transport? Energy 2010;35:4514e21. [4] Ku¨hne R. Electric buses e an energy efficient urban transportation means. Energy 2010;35:4510e3. [5] Schneidereit T, Franke T, Gu¨nther M, Krems JF. Does range matter? Exploring perceptions of electric vehicles with and without a range extender among potential early adopters in Germany. ERSS 2015;8:198e206. [6] Andreasen SJ, Ashworth L, Sahlin S, Jensen HCB, Kær SK. Test of hybrid power system for electrical vehicles using a lithium-ion battery pack and a reformed methanol fuel cell range extender. Int J Hydrogen Energy 2014;39:1856e63. Y. Enhanced fuel [7] Maalej M, Kelouwani S, Agbossou K, Dube cell hybrid electric vehicle power sharing method based on fuel cost and mass estimation. J Power Sources 2014;248:668e78. [8] Hwang JJ, Hu JS, Lin CH. Design of a range extension strategy for power decentralized fuel cell/battery electric vehicles. Int J Hydrogen Energy 2015;40:11704e12. [9] Casolari BL, Ellington MA, Oros JM, Schuttinger P, Radley CJ, Kiley KA, et al. Model study of a fuel cell range extender for a
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120
10
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23] [24] [25]
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0
neighborhood electric vehicle (NEV). Int J Hydrogen Energy 2014;39:10757e87. Sergi F, Andaloro L, Napoli G, Randazzo N, Antonucci V. Development and realization of a hydrogen range extender hybrid city bus. J Power Sources 2014;250:286e95. Cordner M, Matian M, Offer GJ, Hanten T, Spofforth-Jones E, Tippetts S, et al. Designing, building, testing and racing a low-cost fuel cell range extender for a motorsport application. J Power Sources 2010;195:7838e48. Sharer P, Rousseau A. Benefit of fuel cell range extender for medium-duty vehicle applications. In: EVS27 Electric Vehicle Symposium and Exhibition, Barcelona Spain; 2013. Sapienza C, Andaloro L, Matera FV, Dispenza G, Cretı` P, Ferraro M, et al. Batteries analysis for FC-hybrid powertrain optimization. Int J Hydrogen Energy 2008;33:3230e4. De Lorenzo G, Andaloro L, Sergi F, Napoli G, Ferraro M, Antonucci V. Numerical simulation model for the preliminary design of hybrid electric city bus power train with polymer electrolyte fuel cell. Int J Hydrogen Energy 2014;39:12934e47. n Remo n IN, Kær SK. Andreasen SJ, Ashworth L, Menjo Directly connected series coupled HTPEM fuel cell stacks to a Li-ion battery DC bus for a fuel cell electrical vehicle. Int J Hydrogen Energy 2008;33:7137e45. Le Duigou A, Smatti A. On the comparison and the complementarity of batteries and fuel cells for electric driving. Int J Hydrogen Energy 2014;39:17873e83. Andaloro L, Napoli G, Sergi F, Dispenza G, Antonucci V. Design of a hybrid electric fuel cell power train for an urban bus. Int J Hydrogen Energy 2013;38:7725e32. Corbo P, Migliardini F, Veneri O. PEFC stacks as power sources for hybrid propulsion systems. Int J Hydrogen Energy 2009;34:4635e44. Carton JG, Lawlor V, Olabi AG, Hochenauer C, Zauner G. Water droplet accumulation and motion in PEM (Proton Exchange Membrane) fuel cell mini-channels. Energy 2012;39:63e73. Salomov UR, Chiavazzo E, Asinari P. Pore-scale modeling of fluid flow through gas diffusion and catalyst layers for high temperature proton exchange membrane (HT-PEM) fuel. Comput Math Appl 2014;67:393e411. Salomov UR, Chiavazzo E, Asinari P. Gas-dynamic and electro-chemical optimization of catalyst layers in high temperature polymeric electrolyte membrane fuel cells. Int J Hydrogen Energy 2015;40:5425e31. Janßen H, Supra J, Lu¨ke L, Lehnert W, Stolten D. Development of HT-PEFC stacks in the kW range. Int J Hydrogen Energy 2013;38:4705e13. Dustmann C. Advances in ZEBRA batteries. J Power Sources 2004;127:85e92. GT-SUITE. Vehicle driveline and HEV application manual. Gamma Technologies; 2015. Wahiduzzaman S, Kolade B, Buyuktur S. An integrated proton exchange membrane fuel cell vehicle model. Detroit Michigan: SAE World Congress; 2004.
[26] ASTERICS project homepage www.asterics-project.eu/ mainmenu/home.html [accessed 05.07.15]. [27] Millo F, Rolando L, Andreata M. Numerical simulation for vehicle powertrain development. Rijeka: InTech Numer Analysis - Theory Appl 2011:519e40. [28] Husar A, Strahl S, Riera J. Experimental characterization methodology for the identification of voltage losses of PEMFC: applied to an open cathode stack. Int J Hydrogen Energy 2012;37:7309e15. [29] Pukrushpan JT, Stefanopoulou AG, Peng H. Control of fuel cell power systems. Fuel cell system model: fuel cell stack. London: Springer-Verlag; 2004. p. 31e56. [30] Zhang X, Guo J, Chen J. The parametric optimum analysis of a proton exchange membrane (PEM) fuel cell and its load matching. Energy 2010;35:5294e9. [31] Andreasen SJ, Kær SK. Modelling and evaluation of heating strategies for high temperature polymer electrolyte membrane fuel cell stacks. Int J Hydrogen Energy 2008;33:4655e64. [32] Nasri M, Dickinson D. Thermal management of fuel celldriven vehicles using HT-PEM and hydrogen storage. In: Ninth International Conference on Ecological Vehicles and Renewable Energies (EVER), Monaco; 2014. [33] Argonne National Laboratory. Technical assessment of compressed hydrogen storage tank systems for automotive applications. https://www1.eere.energy.gov/ hydrogenandfuelcells/pdfs/compressedtank_storage.pdf [accessed 17.03.16].
Nomenclature BEV: Battery Electric Vehicle FC: Fuel Cell FCEV: Fuel Cell Electric Vehicle FC-RE: Fuel Cell e Range Extender FC-REEV: Fuel Cell e Range Extended Electric Vehicle FEV: Full Electric Vehicle GHG: Greenhouse Gas HEV: Hybrid Electric Vehicle HT-PEMFC: High Temperature e Proton Exchange Membrane Fuel Cell ICE: Internal Combustion Engine ICE-RE: Internal Combustion Engine e Range Extender LD: Light Duty LD-FEV: Light Duty e Full Electric Vehicle NEDC: New European Driving Cycle OCV: Open Circuit Voltage OEM: Original Equipment Manufacturer RE: Range Extender SOC: State Of Charge ZEBRA®: Zero Emission Battery Research Activities ZEV: Zero Emissions Vehicle
Please cite this article in press as: Millo F, et al., Analysis of a HT-PEMFC range extender for a light duty full electric vehicle (LD-FEV), International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.120